Resistors used in integrated circuits, such as Complementary Metal Oxide Semiconductor (CMOS) integrated circuits, typically have a positive temperature coefficient. That is, the resistance of the resistor increases as the temperature increases. However, the use of resistors with positive temperature coefficients is not always desirable. Adding complex circuitry to adjust the temperature coefficient of resistors on an integrated circuit (IC) may increase the cost and/or power requirements of the IC, while decreasing chip density.
A large number of prior art devices have been developed to adjust for temperature variations. Some of those prior art devices include bandgap circuits such as described in Brokaw, “A Simple Three-Terminal IC Bandgap Reference”, IEEE Journal of Solid State Circuits, Vol. SC-9, No. 6, December 1974, pp. 388-393 (“Brokaw”), J. Chen and B. Shi, “New Approach to CMOS Current Reference with Very Low Temperature Coefficient”, Great Lakes Symposium on Very Large Scale Integration (GLSVLSI) '03 Proceedings, pp. 281-84, Washington, D.C., Association for Computing Machinery (ACM) Publishers (“Chen and Shi”), and in U.S. Pat. No. 6,351,111 (“Laraia”). Also, several prior art temperature compensation circuits utilize specialized devices, such as bipolar transistors, Schottky diodes, and/or Zener diodes, such as described in U.S. Pat. No. 3,899,695 (“Solomon”), U.S. Pat. No. 4,114,053 (“Turner”), U.S. Pat. No. 4,229,753 (“Bergeron”), U.S. Pat. No. 4,258,311 (“Tokuda”), U.S. Pat. No. 4,853,610 (“Schade”), U.S. Pat. No. 4,956,567 (“Hunley”), U.S. Pat. No. 5,038,053 (“Djenguerian”), U.S. Pat. No. 5,125,112 (“Pace”). See also U.S. Pat. No. 5,386,160 (“Archer”) (utilizing current mirrors for temperature compensation), U.S. Pat. No. 6,333,238 (“Baldwin”), and U.S. Pat. No. 6,798,024 (“Hemmenway”) (Baldwin and Hemmenway describing fabrication methods for minimizing temperature coefficients). One prior art circuit, described in U.S. Patent App. No. 2007/0164844 (“Lin”), utilizes negative-temperature-coefficient and positive-temperature-coefficient resistors.
Also, many of the prior art devices can compensate for temperature only as a zero temperature coefficient (ZTC) circuit (e.g., Turner and Lin) or combine complementary-to-absolute-temperature (CTAT) and proportional-to-absolute-temperature (PTAT) currents to achieve temperature compensation (e.g., Djenguerian). What is needed is a simple, flexible circuit design that does not require the use of specialized devices to achieve negative, zero, or positive temperature compensation.